Page 277 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

266 CHAPTER 10 Video
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FIGURE 10.23
Pixel aspect ratios of 1:1 and 2:1.
denominator/height count (e.g., 1920 3 1080 for 1080 interlaced “i” or progressive “p” HD video). Further, video definition is described in three levels:
1. Standard Definition (576i (PAL/SECAM) or 480i (NTSC) minimum) 2. Enhanced Definition (576p or 480p minimum)
3. High Definition (720p or 1080i minimum)
The NTSC standard, as originally adapted in 1941, described a 480i resolution at a 60i (60 interlaced is 30 progressive) fps interlaced frame rate. When color was added in 1953, an additional timing factor of 1000/1001 was added to avoid interference between the chroma carrier signal and the sound carrier, reducing the frame rate to 59.94i (60 3 1000/1001) or 29.97p. With the demise of analog television, the need to separate the carrier and sound signals is moot as these are embed- ded digitally (i.e., mooting the need for the 1000/1001 spacing). Expect further evolution of video standards to reflect the new digital format.
Screen resolution is fixed by the vertical frame line count. Aspect is then adjusted to comply with the desired viewing area. As an example, a 480 line resolution with a 4:3 aspect ratio yields a 640 3 480 viewable pixel count while a 1080 resolution with a 16:9 aspect ratio is 1080 3 1920 (width to height).
Interlaced versus progressive: Interlacing of video is a method of doubling the perceived video frame rate while maintaining the same data bandwidth. As stated above, human perception of indi- vidual frames disappears at approximately 16 fps (minimum flicker rate). In early television broad- casts, a method of splitting the picture into two separate interlaced frames allowed the perceived frame rate to go from 30 fps to 60 fps (NTSC) by transmitting one picture frame in two separate half sections. As an example, a 480i picture is 525 (480 viewable) horizontal lines of pixels. If you split these pixels into even and odd number rows, you can achieve the same picture by transmitting the odd number rows (row 1, 3, 5, 7, etc.) totaling 262.5 rows per half-frame followed next by the even number rows (row 2, 4, 6, 8, etc.) (Figure 10.24). This allows the flicker rate to rise to a full 60 fps (59.94, actually, for NTSC), for smoother video quality, while maintaining the same band- width of 30 fps. This allows for enhanced motion perception providing a much smoother video while practically eliminating perceived flicker. A screen capture of one interlaced video frame shows a poor image quality of the individual frame (actually, half-frame) while the video picture (aggregate frames displayed in series) quality is high, demonstrating a capture of only one-half of the frame for the frame grab. Progressive video is simply a full painting of the entire frame upon each rendering (i.e., a frame grab of a progressive video is picture quality). Therefore, 30p is essen- tially equal to 60i, but the picture is of a much higher quality as the image is not distorted by the